Changing the tubes on a SV will change the tone, as it will on any tube amp. However, the tube amp in the SV series is intended to be pretty transparent. The SV series uses full amp and cab models, meaning that the pre-amp, power-amp, and cabinet is fully modeled. The tube amp is just coloring the tone on top of that. It may not have as drastic of an effect as changing the tubes on a regular tube amp.

For example, the 12ax7's in a regular guitar tube amp are fully involved in creating the unique sound, whereas the 12ax7's in the SV are there simply to boost the final fully-modeled signal before it hits the power amp tubes. So, changing the pre-amp tubes on the SV may not have the same amount of effect as it would on a regular tube amp.

When I got my SV, I put in a pair of matched JJ 12ax7's. They were a bit darker, and had just a bit more break-up at volume. I set up all my patches using those, and it sounded great. So, when the time came to change 'em out, I just stuck with another pair of matched JJ's because I didn't want to adjust all my patches. Same for the 6L6's. I used the stock ones, and replaced them with the same.

Some time ago I found a very ineresting topik from someone that retubed a SV112 with EL34 and I did it and works perfectly!!!!!!I can't understand why I can't find this topik again!!!!!!!!!!Did someone delete it?? the link is :

Here's a good read... http://torresenginee.../maprtutse.html They actually have "matched" 12AX7 tubes! Which wont really matter on the SV, but I got them anyway! LOL! I put the 5751 in the phase inverter slot or V2 and a Tung Sol in the "power boost" slot or V1 and then a nice Mullard in the SV Pre. I also put a set of Groove Tube 6L6's in. All of this made a definite improvement on the amps tone. Not like night and day but it is noticeable. Did it about two years ago and it stills sounds great!

I treat all my tube amps the same way now....Mesa 5881s, EL34s, EL84s and SPAX7s (SV MK1, MK2, DT50 and DT25)...However, I use GT-SAGAX7 (balanced inverter) for the inverters...But I cannot tell any difference between the SAG and the SPA in terms of inverter usage...the cost is identical between those...Always had good luck with Mesa tubes since the late 80s.

I retubed mine with JJ Tubes from Eurotubes and it sounded much better. Less harsh and more responsive/thumpier. I couldn't be happier. Mine were practically brand new too. I've just gotten into the habit of switching all my tubes over to the JJ Tubes right away. I also biased the tubes as they were biased a little cold from the factory.